The invention relates to a rotary positive-displacement pump of the type such as is shown in U.S. Pat. No. 3,904,321.
Such pumps are inserted as air pumps and generally run without lubrication. At low rpm, the lubrication problem may be solved by the application of carbon or graphite or molybdenum disulfide; but such means of "dry lubrication" are not sufficient for high rpm.
In order to shut off the pumping action, the known structural type of pump utilizes the pressure generated by the pump, with the vanes being locked in accordance with the outlet pressure. Such a design has the disadvantage, however, that the piston rolling within a housing bore contacts the vane, locked in its retracted position, once per revolution. This produces friction, which is a particular problem at higher rpm. The intermittent noises which thereby arise are also disturbing.